The invention relates to a method and a device for generating a multi-component compound, in particular for dental purposes, by pressing its components out from exchangeable cartridges, which are arranged alongside one another and open into a mixer, by jointly advancing their plungers by means of an electric drive, in which the advance speed is regulated.
In a known method and a known device of this type (EP 1 010 401 A1), the plungers are at first advanced rapidly. When contact with the components then takes place, the resistance increases, and this is detected. The advance speed is then regulated to a lower constant value in order to ensure that the components are pressed out at a uniform speed. However, it has now been found that in many cases it is not sufficient to regulate the advance speed to a constant value, and instead it is also necessary to select the suitable advance speed. The dentist can of course do this by using already known apparatus. However, in most cases he will not succeed in setting the optimum advance speed. Different types of material have very different viscosities or require particular speeds due to processing factors. A universal adaptation does not take sufficient account of the large number of types of material. Depending on the properties of the material, there is an optimum advance and a good and reproducible result of the work. This is all the more so when the mixer used for the two combined components is not a static mixer, but a dynamic mixer driven by an electric motor. The speed too of this electric motor must then be adapted to the special requirements of the components so that the multi-component compound has the optimum properties.
If the advance and/or the speed of the mixer motor is not set optimally, the following problems can arise.                1. An unsuitable ratio of the speeds of advance and mixer shaft results in a non-optimum mixing of the components. Thus, conditions such as processing times and strengths of the impression are only partly achieved or not adequately achieved.        2. Depending on the viscosity of the material type, a wrong speed of the mixer shaft can result in inadmissibly high shearing, which means that the setting behaviour of the compounds is allowed to increase in an uncontrolled manner.        3. If the components have different flow behaviour, incorrect quantities are dispensed by a rigid speed of rotation. These lead to partial hardening or delays in the impression-taking. This can be compensated for or considerably improved by start and stop ramps.        4. If compounds are dispensed too quickly, a deformation of the pressure vessels or cartridges must be expected. The deformation leads to a change in the volume and thus to an inaccurate dosing of the components. This is all the more problematic if, for example, a container deforms more strongly than the second component. The error can impair the mechanical values of the impression and lead to partial hardening.        5. If compounds are used which have to be placed with precision and accurate dosing, an ideal dispensing speed is helpful. By this means, air inclusions and excess dosing are avoided.        